The technical field of this invention is constant velocity joints.
A well known constant velocity joint, used in the drive axles of front wheel drive motor vehicles, is the xe2x80x9cRzeppaxe2x80x9d joint, described in U.S. Pat. No. 2,046,584, in which a driving member and a driven member transmit torque through a plurality (generally 6) of balls captured in longitudinal grooves in the driving and driven member and a cage. The geometry of the arrangement ensures that the balls are always aligned in a plane which bisects the angle between a pair of planes normal to the driving and driven axes of rotation; and constant velocity rotation of the driven member is thus assured, regardless of the joint angle between driving and driven members. As the joint angle increases, however, some portion of the driven member, usually the output shaft, eventually abuts some portion of the driving member to define a maximum joint angle. A variety of design factors and constraints work together to limit this maximum joint angle, and considerable effort has been expended in attempting to increase it. Such increases in maximum joint angle have generally come at the cost of an increase in joint package size, which is not desirable in the crowded engine compartments of front drive vehicles.
A modification of the original xe2x80x9cRzeppaxe2x80x9d design is shown in U.S. Pat. No. 3,879,960 to Welschof et al. The constant velocity joint of this design is undercut-free: that is, the grooves of the outer joint member have a radial profile at the open end which is parallel to the joint axis so that they are not undercut in the longitudinal direction. The undercut-free design of this reference provides a reasonably high maximum joint angle; but an even higher joint angle is desired.
Commonly owned U.S. Pat. No. 6,186,899 shows various constant velocity joint groove profiles which increase joint angle through a corresponding increase in the ratio (Rx) of the ball center radius (BCR) to the inward axial displacement (x) of the ball center relative to BCR, such that Rx=BCR/x=45 and greater at a joint angle of 46xc2x0. It is not always desirable to increase Rx to the required range of 45 and above in order to achieve the higher joint angles.
The constant velocity joint of this invention provides an increase in maximum joint angle, relative to similarly constructed joints of the prior art, without a corresponding increase in joint package size. Thus, for any desired maximum joint angle, the constant velocity joint of this invention allows a smaller joint package size than a conventional xe2x80x9cRzeppaxe2x80x9d joint of the prior art.
The constant velocity joint of this invention has a modified radial groove profile which significantly decreases ball movement radially inward of the ball center radius so that the ball cage may be increased in diameter without a corresponding increase in ball center radius. The radial groove profile provides a required predetermined funnel angle for ball control at the ball centered point of contact but minimal change in distance from the joint center over most of the axially inner side of the grooves in the outer joint member. One embodiment provides an undercut-free dual arc configuration of the ball grooves in which inner and middle arc segments are formed on the ball grooves of the outer joint member having centers of curvature which are axially offset to one side of the joint center and radially offset from one another and which transition into an undercut-free straight section at the open end of the joint. Another embodiment provides an undercut-free groove configuration in which a straight section of the outer joint ball grooves extends from the open end and transitions into a polynomial arc commencing at a transition point axially outward of the ball center plane at zero joint angle and extending inwardly toward an opposite closed end, and wherein the slope of curvature tangent to transition point is between 6 and 10xc2x0.
Both embodiments provide high angulation to the constant velocity joint without requiring an increase in package size of the outer joint member. In each case, the ratio Rx=BCR/x=30 to  less than 45, at 46xc2x0 joint angle, thus achieving high joint angle with a relatively low Rx ratio as compared to the joints described in aforementioned U.S. Pat. No. 6,186,899.